Philip Johnston has been with the Daily Telegraph for more than 20 years. He is currently assistant editor and leader writer and was previously home affairs editor and chief political correspondent.

Intervention in Syria – who decides what would be legal or legitimate?

The geo-political consequences of Western intervention in Syria are complicated enough; but what about legality of a military strike? Sergei Lavrov, the Russian foreign minister, says any action by the US or the UK would be a breach of international law. Is he right and does it matter?

The lawfulness of a proposed Cruise missile or air attack on Damascus is bound to feature prominently in the debate in Parliament on Thursday because so many MPs will recall the way they were misled over Iraq. The legal advice that the Attorney General had provided to the Labour government ahead of the invasion in 2003 became a focal point for those opposed to the invasion. In his diaries, Alastair Campbell claims Lord Goldsmith, then Attorney General, was prevented from telling the Cabinet about his "doubts" on the legal basis for war. But at least there was a UN Security Council resolution in existence covering Iraq, so the question to be resolved was one of interpretation.

In the case of Syria there is no UNSC resolution because Russia will not allow one. Lavrov is correct, therefore, to the extent that under international law intervention is only allowed under Article 2 (4) of the UN charter with the authority of the Security Council.

Even the use of chemical weapons by the Assad regime does not override this article because it makes no distinction as to whether intervention is allowable for reasons of humanitarian assistance as opposed to conquest. Article 2(4) states: “All members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state.” This is, then, a general prohibition on all forms of military intervention – or threats – for whatever reason other than self defence.

However, this is such a restrictive rule that it is often ignored and will be again this time, it seems. Both William Hague, the Foreign Secretary, and Chuck Hagel, the US Defense Secretary, have made the point that, where necessary, humanitarian considerations should trump international law. They certainly did in 1999 when Nato mounted attacks on Serbia in order to force their troops to leave Kosovo without a Security Council resolution, again because Russia would not agree to one.

Reuters reported Richard Haass, president of the U.S. Council on Foreign Relations, as saying: “The UN Security Council is not the sole or unique custodian about what is legal and what is legitimate…To say only the UN Security Council can make something legitimate seems to me to be a position that cannot be supported because it would allow in this case a country like Russia to be the arbiter of international law and, more broadly, international relations.”

A distinction is drawn, therefore, between what is legal and what is legitimate. The international consensus has been (though not in Moscow and Belgrade) that the 1999 Clinton/Blair intervention in Serbia was illegal but legitimate while the 2003 Bush/Blair invasion of Iraq had elements of legality provided by earlier UNSC resolutions but doubtful legitimacy when it became apparent that the reason given for war – the presence of weapons of mass destruction – did not exist.

Where international law is concerned, intervention on humanitarian grounds without Security Council backing is a violation but provided it is proportionate and necessary – two words we will hear a lot in the next few days – it can be considered legitimate.

However, the question then arises as to whether the proposed strikes are being carried out on humanitarian grounds. If they are to reinforce American credibility because President Obama somewhat foolishly set out red lines that have now been crossed or are designed to give one side the upper hand in the Syrian civil war then they would be a breach of international law. Some international jurists have suggested invoking Article 51 of the UN Charter which speaks of "the inherent right of individual or collective self-defence if an armed attack occurs against a member of the United Nations." The argument here is that since Turkey and Israel have had their sovereignty violated by occasional incursions from the Syrian side of the border they could argue self-defence as a justification for military action. But this is unlikely to wash.

It will be hard for Washington and London to argue that surgical strikes designed to teach Assad a lesson because he overstepped the mark with the use of chemical weapons are either legal or legitimate if they fail to alleviate the misery of the Syrian people.